Field of the Invention
The present invention relates to a user equipment (UE) and a circuit-switched fallback (CSFB) method thereof. More particularly, the user equipment of the present invention establishes a learning database dynamically so as to utilize the learning database to determine a priority of the at least one redirection frequency included in a redirection frequency list.
Descriptions of the Related Art
With the development of wireless communication technologies, wireless devices have been widely used. To satisfy users' overwhelming demands for communication, various telecommunication standards have been developed. For example, the long-term evolution (LTE) is one of the most popular telecommunication standards.
The LTE system only provides the packet-switched service for UEs. Under the current telecommunication architecture, when a user wants to use a LTE capable UE to execute a circuit-switched service, the LTE capable UE needs to fall back to another communication system that offers a circuit-switched service (e.g., UMTS) so as to set up a call. However, when the LTE capable UE is handed over from the LTE system to the second generation or third generation (2G/3G) communication system for the circuit-switched service, it may increase a call setup time during the circuit-switched fallback (CSFB) procedure, which is called CSFB latency.
The CSFB latency is mainly caused by a location update and system information reception procedures. More specifically, in case a current location area (LA) where the LTE capable UE is registered is different from a location area to which a 2G/3G target base station belongs during a CSFB procedure, the specification of the LTE system regulates that the LTE capable UE need to perform a location update procedure so that a call setup can be established successfully. However, the extra location update procedure will increase a call setup time, which might degrade user experience. On the other hand, in some communication system architectures, a user would be unable to receive an incoming call if the LTE capable UE is handed over to a 2G/3G target base station that belongs to a different LA and different MSC pool.
Accordingly, an urgent need exists in the art to provide a CSFB mechanism to avoid selecting a base station whose LA is different from the current LA where the LTE capable UE is registered and to reduce the probability of an incoming call failure during a CSFB procedure.